Field of the Invention
The present invention relates to a wafer processing method by which a wafer formed with a plurality of division lines on a front side thereof and formed with respective devices in a plurality of regions partitioned by the division lines is divided along the division lines.
Description of the Related Art
In the semiconductor device manufacturing process, a plurality of regions are partitioned by crossing division lines formed on a front side of a semiconductor wafer having a substantially disk-like shape, and devices such as ICs, LSIs, liquid crystal drivers, and flash memories are formed in the partitioned regions. Then, the wafer is cut along the division lines to divide the regions formed with the devices, thereby manufacturing the individual devices.
As a method for dividing the wafer along the division lines aforementioned, there has been attempted a laser processing method in which a pulsed laser beam with such a wavelength as to be transmitted through the wafer is used, and the pulsed laser beam is applied with the focal point set inside the regions to be divided. The dividing method using the laser processing method is a technology wherein a pulsed laser beam with such a wavelength as to be transmitted through the wafer is applied from one major surface side of the wafer, with a focal point positioned inside the wafer, so as to continuously form altered layers (modified layers) inside the wafer along the division lines, and an external force is exerted along the division lines along which strength of the wafer has been lowered due to the formation of the altered layers, so as to cleave and divide the wafer. This technology is advantageous in that the width of the division lines can be made smaller (refer to, for example, Japanese Patent No. 3408805).
However, in the case of a wafer in which the surfaces of division lines are coated with a metal film, a fluorosilicate glass film, a silicon oxide passivation film (SiO2, SiON), a polyimide (PI) high-molecular compound film, a fluoropolymer film, or a fluorinated amorphous carbon compound film, there arises a problem as follows. When a pulsed laser beam with such a wavelength as to be transmitted through a wafer substrate is applied with the focal point positioned inside the wafer so as to form altered layers (modified layers) inside the wafer along division lines, it is possible to divide the wafer substrate but it is impossible to divide the film coating the surfaces of the division lines.
In order to solve the above problem, there has been proposed a processing method in which a laser beam with such a wavelength as to be absorbed in the film is applied along the division lines from the front side of the wafer, to split the film along the division lines. Thereafter, a laser beam with such a wavelength as to be transmitted through the substrate is applied from the back side of the wafer along the division lines, with the focal point positioned inside the substrate, so as to form altered layers (modified layers) inside the substrate along the division lines (refer to, for example, Japanese Patent No. 5495511).